Speaking of undergarments, this is next one is more from Avengers than Thor but I'm adding it here anyway.

6) So if Loki can magically change his clothes like he does several times in Avengers, then does that mean he's walking around nekkid all the time? and he just makes his closes appear to be there? Good thing he's a frost giant, otherwise that might be a bit chilly.

Yes, I think that Loki must surely be nekkid *all* the time. (Including when he sat on Odin's throne.) That's why he's shirtless in the Simonson run. The Army would not abide by any other arrangement.

(More seriously, it may be that he is wearing a blue shirt and pants like Thor does when he gets exiled and sent through the Bifrost to earth.)